Method for controlling the amount of water filled in a dishwashing machine

Abstract

A method for controlling the amount of water filled in a dishwashing machine through a normally closed valve (18) to carry out a duty cycle of the machine in which the water is sprayed onto the washload items by a circulation pump (10) driven by an electric motor (11). The water is put under pressure by the pump in an intermittent manner with an alternate sequence of pre-set operating periods (T) and pauses (S) during which the motor rotating speed is at its highest value (V 1 ) and lowest value (V 0 ), respectively. The valve (18) is opened in at least one subsequent pause (S) following a preceding period (T) in which the pressure of the water in correspondence of the pump (10) decreases below a pre-determined threshold value (P 2 ).

What is claimed is: 
     
       1. Method for controlling the amount of water being filled in a dishwashing machine including normally closed valve means (18); a program sequence control switch (12) controlling the valve means; spray means (7); a circulation pump (10) supplying the spray means; an electric motor (11) driving the pump and controlled by said program sequence control switch; and pressure sensing means for determining pressure of the water at the circulation pump, the method comprising the steps of: energizing the circulation pump to pressurize the water in an intermittent manner with an alternating sequence of pre-set operating periods (T) and pauses (S) during which a nominal rotating speed of the motor is at its highest value rated (V 1 ) and its lowest value (V 0 ), respectively;   spraying the water on washload items through the spray means;   sensing the pressure of the water at the circulation pump; and   characterized by opening said valve means (18) in at least one pause (S) following a period (T) during which the pressure of the water at the pump (10) decreases below a pre-determined threshold value (P 2 ).   
     
     
       2. Method according to claim 1, characterized in that, prior to said sequence of periods (T) and pauses (S), said valve means are opened for a pre-set period of time (t 0  -t 1 ) so as to enable a partial water filling phase to be carried out in the machine. 
     
     
       3. Method according to claim 1, characterized in that, when the pressure of the water at the pump (10) persistingly stays above said threshold value (P 2 ) until the end (t n ) of at least one period (T), the valve means (18) are closed so as to terminate the water filling process in the machine following a certain delay after said end (t n ) of said period. 
     
     
       4. Method according to claim 1, characterized in that the valve means (18) are closed so as to terminate the water filling process in the machine when the pressure of the water at the circulation pump (10) remains above said threshold value (P 2 ) during at least two successive periods (T). 
     
     
       5. Method according to claim 1, wherein said pressure sensing means is a tachometer arrangement (13) producing a signal that is indicative of the actual rotating speed of said circulating pump driving motor (11) and said signal is delivered to said program sequence control switch (12).